(1) Field of the Invention
The present invention relates to an input circuit, more particularly to an input circuit constructed having a plurality of channels provided with input ports and input/outputs ports and where the plurality of channels deal mainly with analog signals.
(2) Description of the Prior Art
A recent trend in many fields is for automatic data processing and, therefore, for introduction of microcomputers and the like. Such data processing involves a great deal of information. The data is input one by one and successively processed. To input the information, an input circuit having a plurality of channels is usually used. Each of the plurality of channels transfers certain kinds of information, designated thereto in advance, to a predetermined internal circuit at specified timings.
Such an input circuit is fabricated as an integrated circuit (IC). The plurality of channels, each including, for example, one or more metal-oxide-semiconductor (MOS) transistors, must be arranged with a very small pitch therebetween. This, contrary to the desired electrical independence of the plurality of channels, results in increased manual interference between, which produces undesired noise such as crosstalk. The undesired noise reduces the accuracy of the information input to the circuit and the accuracy of the data processing.
The above-mentioned problem will be analyzed in greater detail later, but, in conclusion, it is effective to fabricate the input circuit so as to, first, prevent a high voltage signal on one channel from influencing neighboring channels and, second, make the voltage level of each channel stable.
Conventionally, this is done by arranging the plurality of channels with a relatively large pitch therebetween. This, however, is disadvantageous from the viewpoint of achieving high IC density.